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When you start making your own vinegars there is always the worry that leaving them out at room temperature can cause them to go off and somehow poison you and your family.
Spoilage bacteria growth is inhibited in acidic solutions so homemade vinegar with a pH below 4 is considered safe and doesn’t need refrigeration but acetic acid bacteria continues to acidify vinegar at temperatures above 16 ˚C. To maintain a specific flavor profile refrigeration is recommended.
Whether or not you refrigerate your homemade vinegar depends on your preferences as well as safety concerns.
Refrigeration helps to maintain a constant flavor profile
Unless you pasteurize your homemade vinegar there are still active acetic acid bacteria and yeast cultures living in it. These two have a cooperative relationship. The yeast produce alcohol which the acetic acid bacteria use for food to produce acetic acid. Most yeast cultures cannot live in a highly alcoholic environment with most of them dying off when the alcohol level rises above 4%. The action of the acetic acid bacteria keeps the alcohol level low by using it for energy.
This process will continue as long as there are available sugars in the vinegar which the yeasts can ferment. As the yeasts consume the sugar the vinegar will get less sweet and more acidic. This changes the flavor of your vinegar. Refrigeration slows the action of the yeast and the acetic acid bacteria which helps to maintain a steady flavor profile.
If you pasteurize your homemade vinegar it will remain stable as long as it is sealed but the moment it is opened airborne yeast and acetic acid bacteria will have access to it. The changes will take longer but in time the flavor will change as the new yeast and bacteria start to grow.
To refrigerate your homemade vinegar or not
Homemade vinegar can be made any way you like it sweet, tangy, flavor rich or only slightly flavored. It is very versatile and can be used for a variety of purposes from dressings to drink mixes.
When it comes to deciding whether or not you should refrigerate it consider the following things
How sweet you like your vinegar
Vinegar which still has a high sugar content but has a low enough pH to be considered vinegar can change in flavor and acidity quite rapidly in a warm environment. Yeast species are very acid tolerant and will continue to convert the sugar in the vinegar into alcohol providing energy for the acetic acid bacteria.
Even if the acetic acid bacteria don’t convert any of the alcohol into acetic acid the vinegar will still be less sweet as the yeasts continue to use the available sugars. To slow this process down you can store the vinegar in the fridge. This will slow the yeasts down and the flavor will remain relatively the same. If you want the vinegar less sweet then continue to ferment it until it reaches the desired sweetness.
The vinegar is getting too sour
Vinegar will continue to ferment as long as there is sugar, yeast, oxygen and acetic acid present. This process reduces the amount of sugar in the vinegar making it less sweet and adds acetic acid which makes it sour. To stop this process you have a few options.
Pasteurize your vinegar and store it in a sealed container
Pasteurizing kills off all microorganisms in the vinegar essentially halting the fermentation process. This stops the souring effect of the live acetic acid bacteria. Pasteurization will change the flavor of the vinegar but once it has cooled the flavor will remain stable as long as the vinegar is kept in a sealed container.
Store your vinegar in air locked containers
Acetic acid bacteria need oxygen to grow. When the vinegar is sealed in an air tight container the acetic acid bacteria stop producing acetic acid and the vinegar stops getting sour.
If your vinegar is still high in sugar content use tops which will release air pressure from the container as the yeasts do not need oxygen will produce CO2 gas which will pressurize a sealed container. This can lead to bursting bottles which can be dangerous.
Refrigerate your vinegar
Refrigeration slows the respiration of the yeasts and acetic acid bacteria. This slows the souring of the vinegar. The flavor will stabilize as the microbial action slows down but refrigeration will not stop the fermentation process it will only slow it down so if you leave your vinegar in a fridge for long periods of time you will notice its flavor changing.
Your vinegar has a harsh flavor
Young vinegar can have very hard flavors which stand out. This can be good for vinegars like apple cider or cherry where the tangy flavor and recognizable aroma of the fruit is wanted but when you want a mellow flavor then aging your vinegar in cool temperatures is best.
Aging vinegar is just like aging wine. It should be done at cool temperatures below 16˚C. Unless you have a natural wine cellar then this will require a refrigerator. Some vinegars like Balsamic vinegar is aged in wooden barrels at least 5 years before it is bottled. This produces a sweet tasting thick vinegar with a complex flavor profile.
Other vinegars such as rice wine vinegar also can go through a long aging process which refines its flavor and adds additional aromas.
The alcohol content is too high
Making vinegar is a biological two-step process. The yeasts first need to produce alcohol which is then used by the acetic acid bacteria to produce acetic acid. This process can be broken down into two physical steps by fermenting the fruit into wine and then leaving the wine open to the air. Once the acetic acid bacteria in the wine gets access to oxygen it begins to produce acidic acid which lowers the alcohol content and acidifies the wine.
If you find your vinegar is too high in alcohol then do not refrigerate it. Leave it out at room temperature until the alcohol level has dropped to your liking. Taste the vinegar often as it can sour quickly once the yeast runs out of easily fermentable sugar.
Your vinegar is not tangy enough
Although a liquid can be considered vinegar if it has a pH below 4.0 this does not mean that it will be tangy enough for your purposes. Acids with a pH of 4.0 are very weak acids and when it comes to vinegar it is the acidity which makes it useful.
If youR vinegar is not acidic enough refrigeration will only slow the acidification process down. To encourage the acidification process you can try keeping it at the acetic acid bacteria’s optimum growth temperature of 20-25˚C., aerating it by stirring it and/or placing it in a larger container with a wider mouth.
The optimum temperature will encourage the acetic acid bacteria to grow and stirring it will provide additional oxygen. Placing it in a wider mouthed container will expose more surface area to the air providing more access to oxygen.
Why a pH below 4.0 is important and how refrigeration can affect it
When organic material is left alone it is becomes food for a wide range of microorganisms. These can range from bacteria, yeast and mold. Left alone they will fight for food and space by excreting chemicals which deter the growth of other microbes. This produces a balance which leads to the breakdown of the food source completely adding value to the soil.
One of the most prevalent pathogenic bacteria which is found in every environment is Clostridium botulinum. This is a dangerous bacteria as it produces a toxin which is tasteless. It has a low pH range of 4.6 which means that a pH 4.0 will prevent the growth of this deadly microbe.
Molds are also basic loving organisms which are responsible for producing toxic substances as well as flavors which are unpleasant. A low pH helps to slow the growth of these helping to produce good tasting healthy vinegar.
Refrigerating your vinegar can raise the pH above the recommended value if it is close to the line. This is because acidity is a measurement of available H+ ions, as the liquid cools these ions become less active causing the pH to rise.